Electrical systems in residential, commercial and industrial applications usually include a panelboard for receiving electrical power from a utility source. The power is connected to the panelboard via line bus bars and neutral bus bars. The electrical power is delivered from the panelboard to designated branch circuits through line and neutral conductors supplying one or more loads. Typically, various types of protective devices are mounted to the bus bars of the panelboard to protect the branch circuits from hazardous electrical conditions and reduce the risk of injury, damage or fires.
Circuit breakers are a well known type of protective device which are designed to trip open and interrupt an electric circuit in response to detecting overloads and short circuits. Overload protection is provided by a thermal element which, when heated by the increased current, will cause the circuit breaker to trip and interrupt the power. This can occur when too many loads draw power from the same branch circuit at the same time, or when a single load draws more power than the branch circuit is designed to carry. Short circuit protection is provided by an electromagnetic element that trips when sensing high current flow. Circuit breakers may also provide protection against ground faults which occur when current flows from a hot conductor to ground through a person or object.
Arcing faults, which occur when electric current "arcs" or flows through ionized gas between two ends of a broken conductor, between two conductors supplying a load, or between a conductor and ground, comprise one type of electrical hazard that can not generally be detected by standard circuit breakers. This is because current levels associated with arcing faults are generally not high enough to trip the thermal or electromagnetic elements associated with standard circuit breakers. Arcing faults typically result from corroded, worn or aged wiring or insulation, loose connections, wiring damaged by nails or staples through the insulation, and electrical stress caused by repeated overloading, lightning strikes, etc. The presence of an arcing fault creates a significant fire hazard because it generates heat which may ignite the conductor insulation and adjacent combustible materials.
Arcing fault detection systems known in the art generally sense the current passing through the line conductor of a branch circuit, process the sensed information to determine whether the characteristics of the line current represent the occurrence of an arcing fault, and trip open the branch circuit if an arcing fault has occurred. A preferred arcing fault detection system of this type is described in pending U.S. patent application Ser. No. 08/600,512, entitled "Arcing Fault Detection System", assigned to the assignee of the present invention and incorporated herein by reference. The arcing fault detection system may sense line voltage rather than line current.